[sdiy] Digital Synth Module ideas ...

[Seb Francis]

Andre Majorel wrote:
> On 2006-09-04 11:07 +0100, Seb Francis wrote:
>
>   
>> Andre Majorel posted some samples recently of what it sounds like doing 
>> various bit-swap operations (link anyone?).  Unfortunately again mostly 
>> ugly digital distortion.
>>     
>
> That would be http://www.teaser.fr/~amajorel/aubitswap/. It tends
> to be UDD(tm) when you swap low-order bits with high-order bits.
> Swapping adjacent high-order bits gives more musical spectra. For
> example, try swapping bits 13 and 14 on a full-scale sine. There
> are sound samples on the page.
>
> In general, the resulting spectrum is very sensitive to the
> amplitude of the input signal so it's definitely worth trying it
> post-VCA.
>
>   

Yeah, this is what I found when I tried it out myself (while developing 
the 4xD software, I got curious and tried swapping some high order bits 
around) - depending on the amplitude you go from undistorted to very 
distorted as you cross the bit threshold.  I didn't find it a terribly 
useful or pleasant effect for processing complete sounds, although 
probably it would be quite good with raw waveforms.

This is along the lines of wavefolding, so perhaps could be one of the 
modes of a digital wavefolder module...


> For a hardware implementation of bit swap, I would use an ADC and
> a DAC back-to-back with a patch panel between the two, say 12 jack
> sockets for the top 6 bits. It's intuitive and it opens the
> possibility of doing bit-bashing with external logic modules like
> the CGS26 and CGS39. IMO that would be a better interface than
> anything you might achieve with a micro-controller and a bunch of
> buttons and LEDs.
>
>   

Interesting idea :)  I was intending that the micro-controller be 
voltage controlled, so the interface would not restricted to buttons and 
LEDs, although there would only be a limited number of CV inputs.

>   
>> P.S. Andre, what software did you use to do the bit-swap stuff?  I have 
>> cygwin installed, so I'd like to try out some of these ideas before I 
>> bother coding them in assembler!
>>     
>
> The source code is on the page. It's C++.
>
> If you need the other utilities (auamp, auplot, ausin etc.), I'll
> give you the whole source. They should all be portable except for
> ausink and ausource (audio I/O) which depend on OSS. Everything
> else is a raw PCM. Trivial to convert to and from WAVE.
>
>   

Ah ok .. I was wanting to use some nice unfussy scripting language like 
tcl.  I guess it'd be pretty easy provided the files to be processed are 
raw PCM.  For the plotting & sound gen. functions I'll probably just use 
SoundForge (not that I'm against command line tools - especially when 
you want to batch/script everything :)

Seb